1. Field
This invention concerns drill bit guide devices or jigs and particularly those jigs which are to be employed for properly aligning a drill bit with the screw hole in a hardware item, such as is common in door hinges, latches and the like which have countersunk holes for flat head mounting screws. For such items, if the pilot hole for the screw is not drilled exactly in the center, i.e., axially of the countersunk hole, and if the pilot hole is not drilled exactly perpendicular, i.e., normally to the hardware item, the head of the screw will not be flush with the outer surface of the item when the screw is driven home. The purpose and utility of the present device is to permit one to drill a flat head screw pilot hole that is exactly centered in the countersunk screw hole and exactly perpendicular to the work surface. Also, the present device has universal utility for practically any size countersunk screw hole regardless of the angle and depth of the countersunk walls.
The usefulness of such guides or jigs is well described in the xe2x80x9cTechnical Fieldxe2x80x9d description of U.S. Pat. No. 4,544,307, to wit:
xe2x80x9cWhen flathead screws are used to attach workpieces to backings, extreme accuracy is necessary in the location and entry angle of the pilot holes, so that a jig would be indicated. For, as the heads of such screws are driven home into their countersunk orifice, the position assumed by the workpieces is irrevocably committed, with no compensating possible. When the workpiece is a hinge, an almost imperceptible error in hinge position could be multiplied by the moment arm of the door closure to result in a functional error at the latch side of the door.xe2x80x9d
2. Prior Art
The most relevant prior U.S. patent in this field known to Applicant is U.S. Pat. No. 4,544,307. The jig of this patent however, does not have universal application to countersunk holes and is stated as being specific to a particular workpiece. It is also characterized as having no moving parts. Such construction, as will be seen, is markedly different from Applicant""s device.
Objects, therefore, of the present invention are: to provide a pilot hole drilling guide device which can be used for practically any size and contour of countersunk screw holes; and to provide such a device with structure for automatically axially centering a drill bit with a countersunk screw hole in a hardware item.
The above and further objects hereinafter appearing have been attained in accordance with the present invention which, in a broad embodiment, is defined as a guide device for pilot hole drill bits for use with hardware items having countersunk screw holes, wherein the device provides a drill bit holder which is reciprocably mounted in a body member on a drill axis and which is formed with an abutment end portion, wherein axial position adjustment structure is provided for allowing said end portion to contact the angled wall surfaces of a countersunk screw hole on a plane which is oriented normal to the axis of a screw hole and the drill axis, wherein the body member lies flat on the upper surface of the item.